We will use the power of complete genome sequences and forward genetics to identify novel genes that allow a bacterial pathogen to colonize and persist in the mammalian intestine. Non-typhoidal Salmonella are food borne bacterial pathogens that cause hundreds of millions of cases of diarrheal disease and hundreds of thousands of deaths worldwide each year. Salmonella enterica serotype Typhimurium is an excellent model for study of intestinal fitness because of the availability of complete genome sequence information, the ease of genetic manipulation, and the availability of numerous animal models. We have generated a collection of 1150 targeted deletion strains (approximately 25% of the genome), developed a novel oligonucleotide microarray, and begun forward genetic screening this mutant collection both in vitro and in vivo in murine and chick models. We wish to complete the development of these tools and progress to more comprehensive studies of a subset of genes involved in intestinal persistence and fecal shedding, processes which are critical for transmission of this organism. We will approach this goal by: 1. Completion of our deletion library in all non-essential genes in Salmonella Typhimurium, 2. Screen our deletion collection in murine models to identify new genes involved in intestinal colonization and persistence, 3. Confirm each mutant as defective for intestinal persistence, 4. Characterize mutants that are defective for intestinal persistence.